Blood brain barrier

The brain is a very important organ of the human body and naturally requires special protection. The blood vessels in the brain are covered with a blood-brain barrier (BBB), which helps the brain isolate the infestation of bacteria, viruses and toxic substances in the blood. Except for oxygen, sugar and a small amount of nutrients that the brain needs to pass freely, most of the substances will be isolated outside the barrier, including various proteins and macromolecules.

However, while the blood-brain barrier blocks harmful substances, it also blocks the therapeutic drugs. Whether it is traditional Chinese medicine or Western medicine, most drugs cannot enter the brain, which is naturally not a good thing for patients with brain diseases such as Alzheimer’s disease and Parkinson’s disease.

How to find a drug that can effectively pass through the blood-brain barrier becomes the key to choosing a treatment prescription. In this article, we will introduce Chinese herbal medicines that are commonly used in Chinese medicine and can cross the blood-brain barrier, so as to help you better understand the treatment options of Chinese medicine for brain diseases.

Research Name ：
Studies of blood-brain barrier permeability of gastrodigenin in vitro and in vivo

According to the basic theories of traditional Chinese medicine, Gastrodia elata (GE) is clinically utilized for the treatment of cephalalgia and migraine.

The gastrodigenin (p-hydroxybenzyl alcohol, HBA), one of the effective components of GE, may pass through the blood-brain barrier (BBB) to exert its pharmacological effects. This study aimed to investigate BBB permeability of HBA via in vitro hCMEC/D3 BBB model and in vivo microdialysis in rats. For the establishment of in vitro BBB model, hCMEC/D3 cells were used to construct the monolayer. The integrity of the monolayer was evaluated by TEER measurements, expression analysis of tight junction proteins (claudin-5, zo-1 and occludin) and apparent permeability coefficients (P_app) of fluorescein disodium. During the 6-day incubation of hCMEC/D3 cells, the values of TEER gradually increased and maintained above 100 Ω·cm². Besides, the expression levels of claudin-5 and zo-1 in hCMEC/D3 cells increased over time, and tended to be stable, suggesting that integrity of the monolayer has been completely established. Moreover, the P_app of fluorescein disodium was 3.94 × 10^-7 cm·s^-1 after administration for 180 min, indicating that the monolayer retains the characteristics of BBB and can restrict the diffusion of hydrophilic small-molecule compounds. A sensitive HPLC method was established for HBA detection, and the transport rate of HBA was assessed by a transwell system. HBA crossed the hCMEC/D3 BBB model rapidly, but a plateau was observed when HBA concentrations were relatively similar between the two sides of transwell. Permeability assay revealed that 32.91% of HBA could penetrate the in vitro BBB model after 240 min of administration. In vivo BBB permeability was evaluated by determining the concentrations of HBA in blood and brain simultaneously. Following HBA administration, the samples of microdialysis were collected at 20, 40 and 60 min, and then every 30 min until the procedure ended. Pharmacokinetic parameters of HBA showed that HBA could pass through BBB and reach its maximum concentration at 40 min in blood and brain tissue. Furthermore, AUC_0-t and AUC_0-inf for the brain-to-blood distribution ratio of HBA were 0.1925 and 0.2083, respectively, indicating that approximately 20% of HBA in blood could pass through the BBB and subsequently transported into the brain. Both in vitro and in vivo experiments confirmed that HBA could penetrate the BBB. In summary, the findings of this study highlight that a promising amount of HBA in blood can pass through the BBB and exerts its pharmacological effects on central nervous system (CNS) diseases.

Keywords: Blood–brain barrier; Gastrodia elata; Gastrodigenin; Microdialysis; hCMEC/D3.

Reference：

Yahui Mi, Yukang Mao, Huan Cheng, Guohan Ke, Mingping Liu, Chunping Fang, Qian Wang. Studies of blood-brain barrier permeability of gastrodigenin in vitro and in vivo. Fitoterapia. 2020 Jan;140:104447. doi: 10.1016/j.fitote.2019.104447. Epub 2019 Dec 2.

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